A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Date: 2016 Jul 25, 10:40 -0700
I think it would be easy for almost anyone with a lathe to make the broken screw. Making some wild guesses, it looks like maybe an 10 mm coarse right hand thread on both ends and maybe a 5 mm fine thread hole. I think that the (broken) 10 mm end screws into the sextant frame and the small thumbscrew locks it. Normally the larger thumbscrew would allow mounting and removal of the scope.
You could probably even make one with a vise, hacksaw, drill, tap, and a die. Check the threads first!
If you decide to throw it away, call me. :-)